Why are ducks, geese, and swans called waterfowl?

Ducks, geese, and swans are collectively referred to as waterfowl because they are birds typically associated with freshwater or marine habitats.12

In the United States, the term "waterfowl" is used to describe all varieties of these birds, which belong to the family Anatidae within the order Anseriformes. While the term is sometimes expanded to include other aquatic birds such as loons, grebes, and coots, it is most commonly applied to the members of the Anatidae family due to their reliance on aquatic environments for feeding, swimming, and nesting. In Britain, the term "waterfowl" is often reserved for domesticated species kept for ornamental purposes, while the term "wildfowl" is used for wild populations.123